This invention relates to the sequencing of DNA strands.
In one class of techniques for sequencing DNA, identical strands of DNA are marked. The strands are separated into four aliquots. The strands in a given aliquot are either individually cleaved at or synthesized to any base belonging to only one of the four base types, which are adenine, guanine, cytosine and thymine (hereinafter A, G, C and T). The adenine-, guanine-, cytosine- and thymine-terminated strands are then electrophoresed for separation. The rate of electrophoresis indicates the DNA sequence.
In a prior art sequencing technique of this class, the DNA strands are marked with a radioactive marker, cleaved at any base belonging to a base type unique to the aliquot in which the strands are contained, and after being separated by electrophoresis, film is exposed to the gel and developed to indicate the sequence of the bands. The range of lengths and resolution of this type of static detection is limited by the size of the apparatus.
In another prior art sequencing technique of this class, single strands are synthesized to any base belonging to a base type unique to the aliquot in which the strands are contained. The strands are marked radioactively for later detection.
It is also known in the prior art to use fluorescent markers for marking proteins and to pulse the fluorescent markers with light to receive an indication of the presence of a particular protein from the fluorescence.
The prior art techniques for DNA sequencing have several disadvantages such as: (1) they are relatively slow; (2) they are at least partly manual; and (3) they are limited to relatively short strands of DNA.
In a technique related to DNA sequencing, used to identify restriction fragment length polymorphisms (RFLPs), DNA strands, cut by restriction enzymes, are separated into bands by electrophoresis and moved at right angles onto a blotting matrix containing radioactively labelled probes for identification. This procedure has the same disadvantages as the prior art sequencing procedures.
Digital DNA Typing using radioactivity labeling and transfer by blotting is known in the prior art from Jeffreys, A., A. MacLeod, K. Tamaki, D. Neil, and D Monckton. Minisatellite reseat coding as a digital approach to DNA typing. Nature 354:204-209, 1991. This method of digital typing has the disadvantages of requiring radioactivity, being time consuming and limited on the number of DNA bases that can be considered.